Liquids in various systems are plagued by the buildup of scale and/or corrosion and/or one or more other contaminant materials often due to thermal and/or otherwise caused breakdown of dissolved components and assault of dissolved electrolytes on surfaces, for example, metal surfaces, of the system and/or one or more other environmental conditions. In an effort to mitigate this buildup/contamination, various chemical additives typically are added periodically to the such systems, e.g., whenever liquid is added to the system. The chemical additives include, but are not limited to, anti-foulants, anti-scaling agents, corrosion inhibitors, pH buffering agents, microbiocides, and the like. Usually, the concentration of a particular agent in the system, for example, a cooling system, which can vary due to evaporation, chemical neutralization, and degradation, etc., is not known at any given time. Instead, a predefined amount of additives in a predetermined ratio is added to the system at regular maintenance intervals or whenever liquid levels drop to a level requiring additional liquid.
Various methods of introducing additives to fluid or liquid systems, generally, have been proposed. Rohde U.S. Pat. No. 3,749,247 describes a container for releasing an oxidation inhibitor into hydrocarbon-based lubricating oil in a working engine. The oxidation inhibitor is held in a polyolefin container that permits the additive to permeate through the container wall into the oil. A further approach is described by Lefebvre U.S. Pat. No. 5,591,330, which discloses a hydrocarbon oil filter wherein oxidation additives in a thermoplastic material are mounted in a casing between a particle filtering material and a felt pad. Reportedly, the thermoplastic material dissolves in the presence of high temperature oil thereby releasing the additives. Additionally, an additive release device for use in an engine hydrocarbon fuel line is proposed by Thunker et al U.S. Pat. No. 5,456,217. The latter device comprises a partially permeable cartridge positioned in the filling neck of the fuel tank so that whenever fuel is added a portion of the additive contents of the cartridge is released into the tank.
Aqueous-based liquids present an environment distinct from those of hydrocarbon fluids. For instance, most thermoplastics do not dissolve in aqueous solutions. Moreover, relatively large quantities of additives need to be provided in a typical industrial liquid, e.g., aqueous liquid, such as an industrial liquid used outside an engine or engine cooling system. Sudden provision of such large amounts of additives can cause a “slug” of material to precipitate and circulate in the system, which can result in damage and failure of pump seals. It would be advantageous to provide relatively low cost, quickly installed apparatus and methods that release additive compositions comprising chemical additives into liquid compositions, such as industrial liquid compositions at sustained rates to allow such compositions to function effectively without becoming unduly contaminated or otherwise being detrimentally affected by the additive compositions.